The steadily growing demand for sustainable development is leading to an increasing pressure on building developers and designers to produce buildings with a higher level of environmental performance. Chief amongst environmental impacts from buildings is the consumption of energy from fossil fuels. More than 40% of the total energy consumption in the EU is related to buildings, which means there is significant potential for economic savings. To capture these potential savings the EU has approved the Energy Performance of Buildings Directive (EPBD) which is a regulatory initiative to reduce the energy use in buildings. Furthermore, performance-based requirements in terms of indoor environment, prEN 15251, will be implemented in the EU member countries as well. As a consequence of these new policies, energy performance and indoor environment have become decisive design goals in the building design process. However not many building designers know the consequences of their initial design decisions in terms of energy performance and indoor environment leaving the task of complying with design goals to expensive sub-optimizations at a later stage in the building design process. If buildings are to contribute effectively to sustainable development, new methods and tools which integrate energy performance and indoor environment beginning at the earliest state of the building design process are needed. This seminar will provide an overview of the new regulatory requirements regarding energy efficiency and indoor environment in Denmark and Europe followed by a discussion of a suggested method for the integrated design of new low energy office buildings, and a presentation of a new simulation tool (BuildingCalc/LightCalc) for integrated performance evaluation of office spaces in terms of energy and indoor environment - with special emphasis on daylight simulation.